Charles Darwin recognized that natural selection can make eyes sharper, muscles stronger, and fur thicker. But evolution does more than just improve what’s already there. It also gives rise to entirely new things—like eyes and muscles and fur. To study how new things evolve, biologists usually have to rely on ancient clues left behind for hundreds of millions of years. But in a study published today, scientists at Michigan State University show that it’s possible to watch something new evolve in front of their eyes, in just a couple weeks.

The scientists were studying a virus, which evolved a new way of invading cells. As a result, their research not only sheds light on a fundamental question about evolution. It also suggests that it may worryingly easy for viruses such as influenza to turn into new epidemics. Check it out.

[Image of lambda virus: AJC1 on Flickr via Creative Commons]

A fair number of scientists like to get a tattoo to celebrate their research. Ryan Carney, a biologist at Brown University has taken the practice one step further. He’s gotten a tattoo that shows the key finding of a paper he and his colleagues have just published today. They studied a fossil feather from Archaeopteryx, the iconic bird (or almost-bird). They conclude it looked just like this tattoo.

Carney collaborated on the research with a team of scientists who have developed a method to reconstruct colors from fossils. One source of colors in animals is a cellular structure called a melanosome. Depending on the size, shape, and spacing of melanosomes, they can produce a range of hues. It turns out that melanosomes are incredibly rugged, sometimes enduring for millions of years.

As I wrote in the New York Times in 2009, the scientists first found melanosomes in the ink sac of a fossil squid and then went on to look at a 47-million-year-old bird feather.  Then they went on to look at the feathers and feather-like structures of dinosaurs, reconstructing some of the colors of their plumage. The color pattern, which included stripes and tufts, hints that dinosaurs may have been using their feathers to show off to each other long before they evolved flight. (More details can be found in this story I wrote for National Geographic last year.)

No examination of feather evolution would be complete, of course, without Archaeopteryx. For over 150 years, it’s been at the center of debates about the history of birds–not to mention evolution itself.

The first fossil of Archaeopteryx was a single feather–the one that Carney has turned into a tattoo. It was discovered in 1861 in a limestone quarry near the town of Solnhofen and brought to Hermann von Meyer, one of Germany’s leading paleontologists at the time. As scientists would later determine, this exceptional feather was 145 million years old. Despite its antiquity, the feather looked much like the feathers on the wings of living birds.

The fossil was so extraordinary that Von Meyer wondered if some forger had etched it. After all, Solnhofen limestone was prized for making finely detailed lithographic prints. But then von Meyer compared the slab and the counterslab and found them to be identical.

“No draughtsman could produce anything so real,” he declared.

Even as von Meyer was studying the feather, the quarry at Solhofen yielded another spectacular fossil: an entire animal cloaked in feathers. Word of the fossil spread fast, but only a few scientists got to glimpse the fossil in person. Its owner, a local doctor, was carefully managing the access to his fossil to fuel a bidding war for his entire fossil collection. Those few glimpses were enough to electrify scientists across Germany and beyond. The animal looked in some ways like a bird. It had wing feathers draped from its arms, for example. But other parts of its body looked more like a reptile’s, such as its long bony tail. It was unlike anything alive today.

At the end of 1861, Von Meyer came up with a name to describe both fossils: Archaeopteryx lithographica—the lithographic first bird.

The debut of Archaeopteryx 150 years ago was a case of beautiful timing. Just two years earlier, Charles Darwin had published The Origin of Species, in which he claimed that living animals had evolved from transitional ancestors. “Had the Solenhofen quarries been commissioned – by august command – to turn out a strange being a la Darwin – it could not have executed the behest more handsomely – than in the Archaeopteryx,” wrote the paleontologist Hugh Falconer.

Darwin agreed. “It is a grand case for me,” he confided to a friend.

In later years, more fossils of Archaeopteryx emerged, and it became even more of a chimera. Like a bird, it had feathers on its entire body. But unlike living birds, it had teeth in its mouth and claws on its wings. Darwin’s followers continued to argue that it marked a transition in the origin of birds. But opponents of Darwin and his followers argued that a single species—especially one with feathers no different than those on living birds—did not establish a full-blown transition.

“Their views must be at once rejected as fantastic dreams,” the German paleontologist Andreas Wagner declared.

Wagner turned out to be wrong. A number of bird-like dinosaurs have come to light in the years since the discovery of Archaeopteryx, and researchers have been able to work out many of their relationships to each other. There’s still plenty of debate about just how well Archaeopteryx itself could fly, as well as its precise place in the dinosaur-bird tree of life. Last July fellow Discover blogger Ed Yong wrote about a new study suggesting other dinosaurs were more closely related to living birds than Archaeopteryx.

In a study funded by the National Geographic Society, Carney and his colleagues were able to sample tiny bits of the original, lone Archaeopteryx fossil, housed in a museum in Germany. They examined its melanosomes, comparing them to the melanosomes in 115 living birds. As they report today, the feather was most likely straight black, as you see it in Carney’s tattoo.

While a single feather isn’t enough to reconstruct Archaeopteryx’s entire appearance, it does provide some interesting clues about the animal. The feather was what’s known as a covert, meaning that it was sandwiched in the middle of the wing, covering the primary flight feathers but covered in turn by the feathers at the wing’s leading edge. As a result, it was mostly hidden from sight. So its black color couldn’t have served to attract the opposite sex or to camouflage it from enemies. It’s possible that the whole wing was black, and this particular covert just went along on the evolutionary ride. It’s also possible, Carney and his colleagues speculate, that the melanosomes were serving another function in this particular feather. In living birds, melanosomes can block bacterial infections, and they can also make feathers hard, preventing them from breaking under the forces of flight.

As for the function of black pigmentation on the shoulders of biologists–well, that’s another story.

Reference: R.M. Carney et al, “New evidence on the colour and nature of the isolated Archaeopteryx feather.” Nature Communications 2012 doi: 10.1038/ncomms1642

This Tuesday I’ll be giving a talk at the New York Academy of Sciences about Science Ink–complete with live tattooed scientists!

Here are some of the details…

When: Tuesday, January 24, 2012, 7:00 PM – 8:30 PM. (A reception will follow.)
Where: The New York Academy of Sciences
7 World Trade Center
250 Greenwich Street, 40th floor
New York, NY 10007-2157
212.298.8600

Get $10 dollars off full-price tickets by using the promo code ZIMMER. Register here: http://www.nyas.org/scienceink

See you there!

In yesterday’s New York Times, I wrote about a new paper in which scientists report the evolution of single-celled yeast into multicellular snowflake-like “bodies.” Most (but not all) of the experts I contacted for the story had high praise for the study. (It also won an award when it was presented as a talk over the summer at the Society for the Study of Evolution.) Once the story appeared, however, some scientists took to Twitter to express their skepticism. As much as I like Twitter, this is one of the situations where it fails. You can’t have a conversation about genetics, lab strains versus wild types, etc., in 140 character chunks. At least not very satisfying ones.

So here’s what I decided to do last night. I used Storify to collect the comments of Leonid Kruglyak of Princeton and Michael Eisen of Berkeley, and then passed them on to Will Ratcliff, the lead author of the new study. He then responded. Below you’ll find the Storify tweets, and then Ratcliff’s response. Please continue the conversation in the comment thread. (And be sure to download the paper–it’s open access.)

Will Ratcliff responds:

Well, I don’t buy it that yeast are multicellular in nature. Certainly some yeast in nature form small clusters (like strain RM11), but as far as I know, these are the exception to the rule. Most strains isolated in nature are unicellular, or at most, flocculating (which I still count as unicellular but social). [CZ: "Flocculating" refers to the clumps that unrelated yeast cells form when they starve.]

Our yeast are not utilizing ‘latent’ multicellular genes and reverting back to their wild state. The initial evolution of snowflake yeast is the result of mutations that break the normal mitotic reproductive process, preventing daughter cells from being released as they normally would when division is complete. Again, we know from knockout libraries that this phenotype can be a consequence of many different mutations. This is a loss of function, not a gain of function. You could probably evolve a similar phenotype in nearly any microbe (other than bacteria, binary fission is a fundamentally different process). We find that it is actually much harder to go back to unicellularity once snowflake yeast have evolved, because there are many more ways to break something via mutation than fix it. The amazing thing we see is that we rapidly see adaptations to this adaptation. If we select for more rapid settling, snowflake yeast evolve to delay reproduction until the parent is larger, allowing it settle more quickly. We see the evolution of higher rates of apoptosis as a way to regulate the size and number of propagules produced. We show that the transition to multicellularity in yeast is surprisingly easy, and have no reason to suspect it would be any harder in other microbes with a reproductive process similar to yeast.

In the history of life, single-celled microbes have evolved into multicellular bodies at least 25 times. In our own lineage, our ancestors crossed over some 700 million years ago. In tomorrow’s New York Times, I write about a new study in which single-celled yeast evolved into multicellular forms–completely with juvenile and adult forms, different cell types, and the ability to split off propagules like plant cuttings. All this in a matter of weeks. Check it out.

(The paper is not yet online yet, but here’s the reference: “Experimental evolution of multicellularity,” William C. Ratcliff, R. Ford Denison, Mark Borrello, and Michael Travisano. Proceedings of the National Academy of Sciences. http://www.pnas.org/cgi/doi/10.1073/pnas.1115323109 )

Update: Here’s a Twitter-Storify-blog follow up on some reactions to the study.

Each year, literary agent and science salonista John Brockman poses a question about science and gets a slew of answers from scientists, writers, and other folks. This year’s question is

WHAT IS YOUR FAVORITE DEEP, ELEGANT, OR BEAUTIFUL EXPLANATION?

Brockman got 187 responses, totaling some 126,700 words. A book, you say! Well, if this year is like previous ones, this year’s answers will indeed become a book. But in the meantime, you can browse the answers for yourself, perhaps plucking out those of your favorite people. (Fellow Discover blogger cosmologist Sean Carroll chooses Einstein’s explanation of gravity, for example.)

I found this year’s question particularly thought-provoking. Why is it that we call an equation or a theory “beautiful”? They don’t have pretty hazel eyes. They aren’t desert landscapes. I’m not sure of the answer. Scientific explanations seem to be beautiful if they give sense to confusing complexity in a very short space. Or maybe we just like the feeling we get when we consider how our puny human brains can interpret the universe.

For a lot of physicists, the beauty of an equation seems to be a good hint that it’s probably true. But I’m always a bit suspicious of beauty as a guide to the natural world. A number of contributors selected Darwin’s theory of evolution as their favorite explanation, and there’s no doubt that’s both beautiful and true. But there have been some wonderfully beautiful accounts of the natural world that have proven awesomely wrong. I was reminded of this fact while working on a new version of my evolution textbook (this one’s for biology majors). I was re-researching how scientists first came to appreciate the vast age of our planet, and realized it was a bit more complicated than I had previously appreciated. So that’s what I chose as my answer, which I’m reprinting here in full:

A Hot Young Earth: Unquestionably Beautiful and Stunningly Wrong

Around 4.567 billion years ago, a giant cloud of dust collapsed in on itself. At the center of the cloud our Sun began to burn, while the outlying dust grains began to stick together as they orbited the new star. Within a million years, those clumps of dust had become protoplanets. Within about 50 million years, our own planet had already reached about half its current size. As more protoplanets crashed into Earth, it continued to grow. All told, it may have taken another fifty million years to reach its full size—a time during which a Mars-sized planet crashed into it, leaving behind a token of its visit: our Moon.

The formation of the Earth commands our greatest powers of imagination. It is primordially magnificent. But elegant is not the word I’d use to describe the explanation I just sketched out. Scientists did not derive it from first principles. There is no equivalent of E=mc2 that predicts how the complex violence of the early Solar System produced a watery planet that could support life.

In fact, the only reason that we now know so much about how the Earth formed is because geologists freed themselves from a seductively elegant explanation that was foisted on them 150 years ago. It was unquestionably beautiful, and stunningly wrong.

The explanation was the work of one of the greatest physicists of the nineteenth century, William Thompson (a k a Lord Kelvin). Kelvin’s accomplishments ranged from the concrete (figuring out how to lay a telegraph cable from Europe to America) to the abstract (the first and second laws of thermodynamics). Kelvin spent much of his career writing equations that could let him calculate how fast hot things got cold. Kelvin realized that he could use these equations to estimate how old the Earth is. “The mathematical theory on which these estimates are founded is very simple,” Kelvin declared when he unveiled it in 1862.

At the time, scientists generally agreed that the Earth had started out as a ball of molten rock and had been cooling ever since. Such a birth would explain why rocks are hot at the bottom of mine shafts: the surface of the Earth was the first part to cool, and ever since, the remaining heat inside the planet has been flowing out into space. Kelvin reasoned that over time, the planet should steadily grow cooler. He used his equations to calculate how long it should take for a molten sphere of rock to cool to Earth’s current temperature, with its observed rate of heat flow. His verdict was a brief 98 million years.

Geologists howled in protest. They didn’t know how old the Earth was, but they thought in billions of years, not millions. Charles Darwin—who was a geologist first and then a biologist later—estimated that it had taken 300 million years for a valley in England to erode into its current shape. The Earth itself, Darwin argued, was far older. And later, when Darwin published his theory of evolution, he took it for granted that the Earth was inconceivably old. That luxury of time provided room for evolution to work slowly and imperceptibly.

Kelvin didn’t care. His explanation was so elegant, so beautiful, so simple that it had to be right. It didn’t matter how much trouble it caused for other scientists who would ignore thermodynamics. In fact, Kelvin made even more trouble for geologists when he took another look at his equations. He decided his first estimate had been too generous. The Earth might be only 10 million years old.

It turned out that Kelvin was wrong, but not because his equations were ugly or inelegant. They were flawless. The problem lay in the model of the Earth to which Kelvins applied his equations.

The story of Kelvin’s refutation got a bit garbled in later years. Many people (myself included) have mistakenly claimed that his error stemmed from his ignorance of radioactivity. Radioactivity was only discovered in the early 1900s as physicists worked out quantum physics. The physicist Ernst Rutherford declared that the heat released as radioactive atom broke down inside the Earth kept it warmer than it would be otherwise. Thus a hot Earth did not have to be a young Earth.

It’s true that radioactivity does give off heat, but there isn’t enough inside the planet is to account for the heat flowing out of it. Instead, Kelvin’s real mistake was assuming that the Earth was just a solid ball of rock. In reality, the rock flows like syrup, its heat lifting it up towards the crust, where it cools and then sinks back into the depths once more. This stirring of the Earth is what causes earthquakes, drives old crust down into the depths of the planet, and creates fresh crust at ocean ridges. It also drives heat up into the crust at a much greater rate than Kelvin envisioned.

That’s not to say that radioactivity didn’t have its own part to play in showing that Kelvin was wrong. Physicists realized that the tick-tock of radioactive decay created a clock that they could use to estimate the age of rocks with exquisite precision. Thus we can now say that the Earth is not just billions of years old, but 4.567 billion.

Elegance unquestionably plays a big part in the advancement of science. The mathematical simplicity of quantum physics is lovely to behold. But in the hands of geologists, quantum physics has brought to light the glorious, messy, and very inelegant history of our planet.

[Post-script: Thanks to responses from readers, I can see how this essay is confusing. I added some passages from the papers I cite below down in the comment thread, which I hope can clear things up a bit.]

[Update: For an up-to-date review of the age and formation of the Earth, see this paper [abstract, free pdf] For a great look at Kelvin’s work, see this piece in American Scientist or the more technical paper on which it was based (free pdf).]

[Image: Photo by Hawaiian Sea - http://flic.kr/p/8AyKnC via Creative Commons]

Drew Berry is one of the great movie-makers of the molecular world. He makes gorgeous computer visualizations of DNA, proteins, and the various goings-on inside the cell. Last night I spent a little time watching a new TEDx talk of his just posted online. My first thought was, “Why didn’t I get to see these movies when I was learning about biology as a kid? Life is unfair.” Compared to the flat cartoons of textbooks, or even the crude animations in documentaries of yore, Berry’s work seems to come from some advanced alien civilization.

In case you haven’t seen Berry’s work before, I’ve embedded his lecture here. (You may have heard about him when he got a recent Macarthur “genius” grant.) If you have seen his stuff before, I’d suggest you watch this anyway. And this time, don’t just watch. Listen.

When I first saw Berry’s work a while back, I was immediately gob-smacked. But as I watched his synchronized swimming of molecules a while longer, I realized after a while that I didn’t understand a lot of what was going on. I didn’t know the names of the molecules I was looking at, and, more importantly, I couldn’t tell what a lot of them were doing. The only sense I could make of it all derived from what I already knew.

Berry’s TEDx talk is more satisfying because it’s a talk. You look at the mesmerizing images, and Berry explains what you’re seeing. What’s really interesting is how he–no doubt unconsciously–uses words that switch on the mental eye. When he zooms in on a chromosome, he points out structures passing through it that look “like whiskers,” which act as the “scaffolding” for the cell (the microtubules). He then zooms into the place where the chromosome and microtubule meet, the kinetochore. What you see looks like a supercomputer’s acid trip. But you can make sense of what you see because Berry uses metaphors. He calls it a “signal broadcasting system.” Now all the molecules jittering around aren’t totally random. We can see how molecules come together to make life possible.

There’s no question that people like Berry are going to be making the movies that fill our heads in our future when we think about what’s going on in our bodies. But those movies will need good soundtracks.

Cancer evolves. Those two words may sound strange together. Sure, birds evolve. Bacteria evolve. But cancer? The trouble arises from the fact that cancers, unlike birds and bacteria, are not free-living organisms. They start out as cells inside a person’s body and stay there, until they’re either wiped out or the person dies.*

Yet the same forces that drive the evolution of free-living organisms can also drive cancer cells to become more aggressive and dangerous. Evolution becomes our inner foe if mutations disable a cell’s self-restraint. The cell multiplies. Sometimes a new mutation arises in its descendants. If the mutations allow the cancer to grow faster, the cells carrying it will take over the population of cancerous cells. Natural selection and other processes that drive evolution on the outside start driving it on the inside.

Like so many other scientists, researchers who study cancer evolution have jumped on new technology for sequencing genomes on the cheap. They’re now starting to publish fine-grained histories of the disease, tracking individual mutations as they arise and spread. Nature has just published a fine example of this new research. I particularly appreciated the informative pictures they came up with to accompany the paper, one of which I’ve included here. You can click on the picture for a bigger version. And below the picture, I’ll explain what it means.

In the new paper, Li Ding and colleagues at Washington University describe a study they carried out on eight people suffering from acute myeloid leukemia (AML), a disease of the immune system. In people with AML, stem cells in the bone marrow that would normally turn into white blood cells instead become cancerous. Treatments include bone marrow transplants and chemotherapy. Unfortunately, AML has a nasty way of bouncing back from chemotherapy, and the drugs become useless to stop it. As a result, a lot of people who seem at first to be in remission eventually die of the cancer.

The Washington University scientists reconstructed the history of the cancer in each patients by sequencing genomes from a number of cells. To determine the normal, original genome, they sequenced DNA from a healthy skin cell. They then sequenced genomes from cancer cells taken from the patients when they were first diagnosed. And then they looked at genomes of cancer cells that emerged after the patients relapsed. From this survey, they came up with a catalog of new mutations that emerged over the course of the cancer. They could then go back into the blood samples and estimate what fraction of the cancer cells had a given mutation at a given point in time.

This figure illustrates the sad chronicle of one particular woman they studied. When she was in her late 50s, she suddenly came down with a sore throat and began to bruise easily. A bone marrow biopsy confirmed she has AML. She got chemotherapy, and then a stem cell transplant. Although she seemed to go into complete remission, the cancer returned 11 months after her diagnosis. The chemotherapy drugs that had previously been so effective now could not stop the cancer. Other drugs failed, too. Two years after her diagnosis, she died.

On the left of the figure, the cancer begins. A single stem cell mutated and became the founder of the cancerous lineage. we start with normal cells. (The cell is dark, and the grey dot marks its original mutation. HSC stands for hematopoietic stem cells).

The cancer cells grew in number, and as they did, they accumulated a lot of mutations, some of which are listed in the figure next to the star. All of these mutations, one after the other, took over the entire population of cells–a signature of natural selection. When the woman went to her doctor, however, the cancer had diversified into a number of different lineage, each carrying additional, distinctive mutations. Over half of the cells belonged to a lineage marked here in purple, known as cluster 2. Cluster 3, marked in yellow, was made up cells with a separate set mutations. And from within Cluster 3 emerged yet another lineage–Cluster 4, marked in orange. The dots in each circle show the sets of mutations that accumulated in each cluster.

The chemotherapy knocked down all the clusters of cancer cells to such low numbers that doctors couldn’t find them any more. But they were still there. And when exposed to chemotherapy drugs, the most successful cluster was not the one that had been most successful back when the cancer was diagnosed. It was the relatively rare Cluster 4. Apparently, it had mutations that made it better able to withstand the chemotherapy drugs. Some its descendants later picked up new mutations, which enabled them to reproduce quickly and take over the cancer population, as they resisted new chemotherapy drugs as well.

“The AML genome in an individual patient is clearly a ‘moving target,’” the scientists right conclude. “Eradication of the founding clone and all of its subclones will be required to achieve cures.” Easier said than done, of course. The parallels between this research and studies on antibiotic resistance in bacteria are sobering. But at least now we’re starting to see what kind of evolutionary challenge we’re really up against.

(*For one very cool exception to this rule, consider the case of Tasmanian devil facial tumors, which travel from devil to devil. They evolve too, though.)

Over on Facebook, David Hillis, an evolutionary biologist at the University of Texas, took up my question as to whether anyone can define life in three words. His short answer was no, but his long answer, which I’ve stitched together here from a series of comments he wrote, was very interesting (links are mine):

Like all historical entities (including other biological taxa), it is only sensible to “define” Life ostensively (by pointing to it, noting when and where it began, and following its lineages from there) rather than intensionally (using a list of characteristics). This applies to the taxon we call Life (hence capitalized, as a formal name). You could define a class concept called life (not a formal taxon), but then that concept would clearly differ from person to person (whereas it is much less problematic to note examples of the taxon Life). So, I’d say that I can point to and circumscribe Life, and that it the appropriate way to “define” any biological taxon. A list of its unique characteristics is then a diagnosis, rather than a definition. So, I’d argue that any intensional definition of Life is illogical (does not recognize the nature of Life), no matter how many words are used.

Defining Life (the taxon) is like defining other particular historical entities. We don’t “define” Carl Zimmer or the United States of America by listing out their attributes. Instead, we point to their origin and history. The same should be true for Life. If we ever discover a Life2, we’ll have a new origin and history to point to.

The question people actually want to ask is “Are there entities in the universe that are similar to the Life we know about here on Earth?” The answer, of course, depends on what people mean by the arbitrary meaning of “similar”. One person might answer “I mean ‘self-replicating with variations’.” Then, the answer is yes: humans have created imperfectly self-replicating systems (“artificial life”) here on Earth. But then someone else says “But that is not what I meant by similar…I meant that they had to have metabolism and cellular structure and a nucelic-acid-based genetic system.” OK, then we have to keep looking to find something that similar. But then someone else says “But that’s pretty arbitrary…I’d still consider it alive if it didn’t have cellular structure.” Exactly…it is indeed arbitrary to argue over how similar something has to be to consider it “similar” to Life. So, in the end, we can ostensively define Life (by referencing its origin and history), and we can do the same for other historical entities that some people might also want to say are alive, but there can be no simple “right” answer that will satisfy everyone about which entities should be considered alive, because we all emphasize different characteristics in defining an arbitrary class concept of “life”.

I’ll be on National Public Radio’s Science Friday this week to talk about Science Ink. Host Ira Flatow and I will be chatting during the 3 pm EST hour. In the meantime, the folks at Science Friday have set up a slide show preview.

We are all sure we know what life is, but if you try to actually define it, things get tricky fast. I wrote a feature about the scientific struggle to define life in 2007 for Seed, and I’ve been keeping tabs on the evolution of this metaphysical quandary ever since. I was particularly intrigued to discover recently that one scientist thinks he can define life–and do so in just three words. I’ve written an essay about his short and sweet definition for the web magazine Txchnologist. Check it out.

Today, a company called Ion Torrent announced they were going to start selling a DNA-sequencing machine that can sequence an entire human genome for $1,000. It’s just the latest milestone in the long-term crash in the cost of gene-reading. There are lots of benefits that will flow from this ongoing transformation. For one thing, as I wrote in 2010 in the New York Times, it’s getting easier to identify new viruses that could turn to be the next HIV or SARS.

To research my story, I paid a visit to the Center for Infection and Immunity at Columbia University. On the day I dropped by, Ian Lipkin and his colleagues were very busy:

Some researchers were examining New York flu, others African colds. The blood of patients with mysterious, nameless fevers was waiting to be analyzed. There was dried African bush meat seized by customs inspectors at Kennedy Airport. Horse viruses, clam viruses: all told, members of Dr. Lipkin’s team were working on 139 different virus projects. It was, in other words, a fairly typical day.

Some of the research that was going on that day–specifically, the research on JFK bushmeat–was published today in the journal PLOS One. The Columbia researchers collaborated with a network of other scientists at the Centers for Disease Control, the Wildlife Conservation Society, Tufts University, the American Museum of National History, and the EcoHealth Alliance to do the first pilot study of the viruses that are carried from country to country by the wildlife trade.

They undertook the study because many of the world’s worst diseases are the result of pathogens switching from animal hosts to us. HIV started out as a chimpanzee virus, which first infected hunters in Cameroon. SARS started in bats, and then spread to palm civets, which then transmitted the virus to people in Chinese animal markets. There’s no reason to think that we’ve seen the last virus jump to our species. So scientists are starting to set up monitoring programs, in the hopes of reducing the chance that the next spillover is not a complete surprise.

As illustrated by HIV and SARS, a lot of viruses come our way through trade in animals. At first, this trade was small-scale. A hunter might come out of the jungle and barter some monkey meat for shoes. Chinese animal markets bring animals from hundreds of miles away. And today, with planes hopping between continents every day, the wildlife trade is now moving animals–and the viruses they carry–around the planet. About 120 million live animals are illegally imported into the United States every year, along with 25 million kilograms of meat and other wildlife remains. The animals that customs agents seize come most often from countries such as China, Hong Kong, and Nigeria–countries that plagued with some of the most worrisome animals viruses, such as Nipah virus and the H5N1 bird flu. It’s likely that West Nile virus first came to the United States in a bird destined for the pet trade; after first showing up in 1999, it’s now found throughout much of the country. Yet nobody has systematically looked at the viruses being brought into the United States through the bushmeat trade.

The authors of the new study studied wildlife products seized  by customs agents at JFK airport between 2008 and 2010, and later also looked at additional seizures in Philadelphia, Washington, Houston, and Atlanta. (The gruesome picture above, from the paper, is a primate head seized at JFK.) All told, they looked at 44 animals. Nine were primates, and the rest of were rats. The scientists isolated DNA from the meat to identify which species it came from. Their sources including chimpanzees and several species of monkeys.

The scientists then fished for genetic sequences of viruses. As they report today, they found a bunch. All nine primates the scientists studied had viruses in them–a variety of simian foamy viruses, cytomegaloviruses, and lymphocryptoviruses, all of which have worried scientists for their potential to cross over from animals to humans.

Since this was just a preliminary study, the scientists did not run experiments to see how well the viruses could infect human cells. So we don’t know if these viruses posed any threat to humans. But that’s no reason to get complacent. The scientists only studied nine primates, after all–a tiny sample of the torrent of primate bushmeat that comes into the country each year. And then there are the swarms of reptiles, mammals, and birds that come into the country as well, carrying potentially dangerous viruses that the scientists didn’t even look at. If people going through customs had to declare all the animal viruses they were bringing into the country, the list would likely be frighteningly long.

(For more information, see my book, A Planet of Viruses, my podcast interview with one of the study co-authors, Peter Daszak, and The Viral Storm by Nathan Wolfe.)